'You need to restart your computer' happening all the time

Got my 15" macbook pro in August, no problems until about a week ago. At least 2 times a day, sometimes 4 times in 1 hour, the screen gradually goes gray and a box pops up telling me I need to restart the computer. Can't use the trackpad or anything. Upon restarting the computer, I get a box telling me I shut down the computer with the following information:

I have removed any programs I have installed that I do not trust 100%. I think the problem may arise from 2 weeks back, where a friend of mine wanted to transfer files to his PC. Did it through a router which was connected to the internet, and it turned out he had turned my firewall off while he did it.
Other problems include not connecting to wireless(used to connect to my network absolutely fine), taking longer to open programs, some programs always asking for permission to keychain access for something or other, when they never used to.

What should I do? Currently, reinstalling os x isn't an option because I can't find the CD for it! Otherwise, I'm gonna have to book a genius appointment somewhere.

Looks like the Airport card causing it. What version of OS X are you using? If you have not upgraded to 10.6.5 yet, try that. If you have upgraded to 10.6.5, when did you do that in relation to the kernel panics beginning.

If you are on 10.6.5, head for System Preferences - Network - highlight AirPort on the left - on the right next to Status go ahead and select Turn AirPort Off.

cheers for the advice bob. sorry, should have mentioned what version of os x i was on. version 10.6.5 updated on the 19th november, which must be near enough when the problems started.
if i could, i would roll back to 10.6.4 but unfortunately i haven't been backing things up (will be starting once I have this fixed tho!)

some progress made. macbook has not had a kernel panic for a couple of days now, and wireless is pretty much working once again (occasionally drops connection or asks for login info for my default network again)

The bad news:
it's running really, really slow compared to how it should run. I normally have it running about 8 applications at the same time, and it seems to be struggling with some things at the moment. safari in particular is very slow.
is there anything I can do to improve it? the only thing i can think of it to download some software to defrag the drive

Make sure you are not using a hidden SSID on your router and that you are using WPA or WPA2 encryption - not WEP

Click the AirPort icon on the menu bar and rejoin your network.

Quote:

The bad news:
it's running really, really slow compared to how it should run.

What does this mean?
You're seeing the beach ball a little more often?
It's taking a second or two longer to open apps?
When you open an app or click on something it's taking several minutes?

Quote:

I normally have it running about 8 applications at the same time, and it seems to be struggling with some things at the moment. safari in particular is very slow.

What 8 apps? What processor load do those 8 apps require? Safari is loading slow or flash content sites are loading slow? Have you opened up Disk Utility to take a look at your stats to see which app is burning CPU cycles (in Applications - Utilities).

Quote:

is there anything I can do to improve it? the only thing i can think of it to download some software to defrag the drive

Need a lot more answers as you can see.

I am one of the few proponents of defragging OS X around here and I would say it is extremely unlikely that you need to defrag a 3 month old machine. What is the size of your OS X partition and how much free space do you have?

I cannot be held responsible for the things that come out of my mouth.
In the Windows world, most everything folks don't understand is called a virus.

jinxed it, another kernel panic about 5 minutes after I posted. Have done very very little beside trying to avoid using the wireless. When I had the last panic, it was connected to wireless. using WPA2 and have done as you said.
It's taking longer to open apps, close apps etc. Such as opening iTunes, now takes about 5 seconds longer than it did. Not a major problem I know, but I would like to get things back to the way they were.

flash content sites taking slightly longer to load, and safari very slow to quit and have had to force quit it a few times in the past few days.
apps like word, pages, safari, ichat, itunes, taco html edit, mail, firefox. nothing too processor heavy there, is there? see attachment for screenshot of activity monitor.

my main concern is stopping the panics, because it's getting annoying having to save my coursework every minute because I don't know when my mbp will next decide it needs to be turned off!

some progress made. macbook has not had a kernel panic for a couple of days now, and wireless is pretty much working once again (occasionally drops connection or asks for login info for my default network again)

The bad news:
it's running really, really slow compared to how it should run. I normally have it running about 8 applications at the same time, and it seems to be struggling with some things at the moment. safari in particular is very slow.
is there anything I can do to improve it? the only thing i can think of it to download some software to defrag the drive

Here's a good question - how much disk space do you have free? If it's not above 20GB, that's why your machine is running super slow.